1. Field of the Invention
The present invention relates to an image reproducing apparatus capable of rapidly transferring and fixing toner image on a charge receptor to a transfer member.
2. Description of the Prior Art
Generally, the image reproducing process using an iamge reproducing apparatus has the steps of forming, on a charge receptor making use of a photoconductive member, an electrostatic latent image corresponding to the document image of the document by a corona charging and projection of light, and forming a visible image by developing the latent image by a developer mainly consisting of colored minute powders of a thermoplastic generally referred to as "toner".
The visible image on the charge receptor, i.e. the toner image, is transferred to a transfer member by an electric process such as corona discharge, bias roller or the like, or mechanical means such as pressing or heating.
The toner image thus transferred to the transfer member is fixed by an ordinary heating means to complete the image forming process.
As stated above, electric process is usable as one of the measures for transferring the toner image on the charge receptor to a transfer member or the like. This method, however, suffers only a low efficiency of transfer and tends to incur disturbance of transferred image particularly when the transfer is made in the atmosphere of high humidity. To avoid this problem, transfer method which does not rely upon the electric process has been developed, such as transferring technique employing pressing, as disclosed in Japanese Patent Application Laid-open to public inspection No. 78,559/1974, and U.S. Pat. No. 3,591,276 and so forth.
For instance, according to the description made in Japanese Patent Application Publication No. 41,679/1971, the toner image on a photosensitive member is held in an elastic and heat resistant intermediate blanket to permit a transfer without leaving any toner image on the photosensitive member thereby to achieve a high quality of transferred image.
In the transfer technique disclosed in the above-mentioned prior art, however, there are following disadvantages. Namely, since the transfer and fixing of the toner image from the intermediate image carrier to the transfer member are achieved simultaneously by the application of heat and pressure, a large heat input is required for the fixing, resulting impractically in an increased consumption of electric power. The large heat input also deteriorates the mechanical durability of the intermediate image carrier and roller used for the transfer and fixing.
The current demand for higher speed of image reproduction requires correspondingly increased speed of fixing. To cope with this demand, various attempts have been made. For instance, it has been attempted to increase the electric power input to raise the temperature of the heating roller. Alternatively, the heat source is incorporated in the pressure roller itself, or the pressure roller is heated by an external heat source. All of these attempts, however, have problems concerning the electric power consumption and cost.
The above-described problem concerning the requirement of higher fixing speed equally applies to the image reproducing apparatus of the type in which the toner image is directly transferred to the transfer member without using any intermediate image carrier.